1. Field of the Invention
The present invention relates to filled polyolefin compositions having improved thermal stability characteristics, and, in most cases, improved color.
2. Description of the Prior Art
Fillers have been used in polyolefin polymers to impart such effects as improved dimensional rigidity and lower costs to the resulting blend of filler and polymer. Such filled polyolefin compositions find utility in a wide variety of applications, including in the manufacture of various formed and molded articles, e.g., appliance components, under-the-hood automotive parts, and instrument housings. However, use of these polymers at relatively high service temperatures has sometimes resulted in thermal degradation of the polymer/filler blend. Also, the use of certain types of fillers in polyolefin polymers result in a blend having a color that is darker than desired. Various approaches have been used to improve the thermal stability and color characteristics of such filled polyolefin compositions.
U.S. Pat. No. 3,425,980 to B. O. Baum advocates the use of a non-acidic, oxygen-containing hydrocarbon or halogenated hydrocarbon to coat clay fillers contained in polyethylene compositions to yield novel white and colorable polyethylene compositions.
U.S. Pat. No. 3,553,158 teaches the use of a variety of "talc deactivating compounds" including such organic polar compounds as epoxides, amides, acrylate polymers and aliphatic polyols to improve the thermal stability of talc-filled polypropylene.
More recently, Japanese Kokai No. 77 45,644 (as abstracted in Chem. Abstr., Vol. 87, 54094y, 1977) teaches a heat resistant polyolefin resin containing filler and a mixture of polyoxyalkylene acid phosphates and a sulfur-containing compound of the formula C(CH.sub.2 OCOCH.sub.2 CH.sub.2 SR).sub.4, where R is a C.sub.10 -C.sub.20 alkyl group.